The invention relates to a protection box for a measuring instrument assembly as used in a process plant and, more particularly, to a tight, sealable reception of part of the measuring instrument assembly in at least one wall of the protection box.
In chemical and refining plants measuring instruments used in the field such as measuring transducers for example, are usually enclosed in protective housings made of a synthetic material. The housing protects the instruments from climatic influences and aggressive substances to ensure its operation and long life. Furthermore these protective housings are provided with heat barriers and heating elements, depending on requirements and circumstances.
Prior protective housings are known in a great number of designs. Current designs consist of a box-shaped part open on one side and of a cover which is placed over the first part in the manner of a hat with intercalation of seals and is attached with quick-acting closures. In another known embodiment (DE 37 04 015 A1) a box-shaped protective housing is divided into two housing parts along the diagonal of the lateral surfaces.
These relatively large protective housings are fixedly mounted on supports in a permanent, immovable manner, and instruments are then placed in them as required. For this purpose holding devices such as C-rail arrangements are provided on which the instruments are mounted. Entrances and exits for process lines and cables are installed individually, and care must be taken for proper installation and sealing. In these known protective housings the installed instruments are thus fixedly connected to a housing part. The housing part is in turn connected in a stable manner to a bearing structure. Attaching such protective housings, and, in particular when installing a measuring instrument assembly after mounting of the protective housing involves considerable assembly work and is accordingly expensive.
Protection boxes of this type to be mounted and held directly at a measuring instrument installation in a process plant, in particular for rapid mounting an already existing measuring instrument assembly are known. These relatively small protection boxes enclose the measuring instrument equipment rather tightly, by contrast to the large protective housings mentioned earlier, and are suited for repeated, tight sealing of at least part of the measuring instrument equipment.
A protection box of this type consists of two box parts in form of half shells made of a solid wall material. The half shells are being connected to each other by latch elements at side rims used as contact rims. The open sides of the half shelf fit together and can be taken apart. Recesses which are open towards the contact rim are provided in the area of one contact rim. These recesses are closed by the fitted second half shell, and possibly by corresponding assigned additional recesses at the adjoining box side of the second half shell, to define a passage opening. The half shells can therefore be placed from both sides on an existing measuring instrument assembly and can be closed. Part of the measuring instrument assembly may be extended through the passage openings in a flow-through arrangement.
A method of enclosing a measuring instrument assembly in a flow-through arrangement with a protection box is known. In that method, a medium-loaded differential pressure measuring cell is surrounded by the two halves of the protection box so that a measuring head emerges from a tailored passage opening of the protection box and where two process lines go into the protection box through separate, tailored passage openings. The measuring instrument assembly is installed in the protection box and is held mechanically.
The installation of such a protection box merely by placement and connection of the two half shells on the measuring instrument assembly works well, is simple and economical. However, the multiplicity of different instruments and different geometries of connections and lines presents a problem. A plurality of different box designs with different slits and opening arrangements for passages with different diameters and in different sizes must be provided. This causes manufacture, due to a plurality of production forms, as well as warehousing, transportation and logistics to be expensive. The advantage of easy installation becomes only a relative advantage.
A further disadvantage of these known protection boxes consists in the fact that as a rule either leaky gaps remain open at the passage openings due to an inaccurate fitting, or that the openings must be sealed manually through individual, expensive measures. The gap between two process lines remains open for example if two half shells with slits are fitted from both sides over the process lines.
Because it is necessary to take into account the variety of equipment in measuring instrument assemblies it is not uniformly possible to produce all box parts in form of economic identical parts so that uniform, volume-saving stacking of one in the other is also impossible.
Another disadvantage may also consist, depending on the application, in that the two box shells can be attached on the measuring instrument assembly only as separate, and not permanently, connected shells. The shells must be removed completely in two parts and must be mounted again upon completion of work when performing maintenance or servicing. This renders handling more difficult. The known connection of the two box parts by means of holding bands is also expensive and inconvenient.
Accordingly, an object of the instant invention is to provide a protection box in such manner that more economic production and handling is possible while its function is improved.